Anion-pi interactions in bisadenine derivatives: a combined crystallographic and theoretical study.

Abstract

[eng] In this manuscript we report a high-level ab initio study of anion-ð interactions involving N9-methyl-adenine, N6- methyl-adenine, N9-methyl-hypoxanthine, a dimer of N9-methyl-adenine, and N9,N9¢-trimethylene-bisadenine. DNA bases like adenine are electron-deficient arenes that are well suited for interacting favorably with anions. We demonstrate that these compounds are able to interact favorably with anions. N9-Methyl-adenine, N6-methyl-adenine, and the dimer of N9-methyl-adenine interact with the anion via the six-membered ring more strongly than adenine due to cooperativity effects between the noncovalent ð-ð and anion-ð interactions. This pattern, i.e., coexistence of ð-ð and anion-ð bonding, is observed experimentally in the solid state. Finally, we report the solid-state characterization of two new compounds N6,N6¢-dimethylene-bisadenine hydrochloride and an outer-sphere complex of protonated N9,N9¢-trimethylene-bishypoxanthine with zinc tetrachloride anion, that exhibit interesting anion-ð interactions. They are in strong agreement with high-level theoretical calculations.